1. Field of the Invention
The present invention relates to a video signal encoding apparatus equipped in a digital camera, a digital video camera, an apparatus for managing images of a monitor camera, computer or; the like, and to a video signal encoding method. More particularly, the present invention relates to a video signal encoding apparatus and a video signal encoding method for converting a compression frame image information group encoded by an intra-frame encoding method into compression moving image information encoded by using both an inter-frame prediction encoding method and the intra-frame encoding method.
2. Related Background Art
Recent digital-cameras practically used have in addition to a still image photographing mode, a moving image photographing mode (intra-frame encoding method such as motion JPEG and MPEG1/2/4) and a voice recording mode.
In the compression encoding method for still images photographed with a digital camera and moving images photographed with a digital camera, a monitor camera and the like, the intra-frame compression encoding method is used which applies a compression algorithm only to only a single image. The JPEG format, JPEG2000 format and the like are typical intra-frame compression encoding methods. In the moving image compression method aiming at a high compression ratio, a compression method is used which incorporates both the inter-frame prediction encoding and intra-frame encoding methods. The MPEG format is a typical moving image compression encoding method. The essential different point between the still image compression method and moving image compression method lies in whether or not the inter-frame prediction is performed.
It has been proposed to apply the inter-frame prediction encoding frames capable of subjecting to the inter-frame prediction encoding process, as an approach to converting a still image format into a moving image format (refer to Japanese Patent Application Laid-Open No. 2001-78199). This approach detects a motion and a motion direction by using DCT coefficients of input compression data to reduce the amount of a process of obtaining a motion vector. Namely, frames having a motion detection result “with motion” are subjected to motion direction detection to perform the inter-frame prediction encoding process, whereas frames having a motion detection result “no motion” are not subjected to motion direction detection (without performing a process of obtaining a motion vector) to perform the intra-frame prediction encoding process.
As different from conventional analog cameras, digital cameras are not necessary to use films so that photographers have a tendency that a number of frames are photographed without any fear of failures or frames are photographed consecutively. Still images of a large number of digital photographs photographed in such a manner are likely to be confirmed, for example, on a liquid crystal display or the like built in the camera, and thereafter unnecessary still images are selected and deleted from a memory to leave only necessary images.
Depending upon such a use state of digital cameras, even if motion detection using DCT coefficients of input compression data is performed for a photographed image (still image) group of a digital camera, there is a high probability of a motion detection result “no motion”. It is therefore inefficient to perform the motion detection process for the entirety of the still image group, prolonging the process time. It has been desired to develop an apparatus capable of performing motion detection more efficiently.
If the format of one still image is converted into the format of one moving image frame and the moving image after format conversion is reproduced in real time, the display time of each frame image is too short and the image contents cannot be admired.
Further, for example, a photographed image group or the like of digital photographs photographed consecutively has often analogous image contents. Therefore, if the format of one still image is converted into the format of one moving image frame and the moving image after format conversion is reproduced in real time, the display time of a plurality of analogous images is too long and the viewer may feel uncomfortable.